The semiconductor industry has seen tremendous advances in technology in recent years that have permitted dramatic increases in circuit density and complexity, and equally dramatic decreases in power consumption and package sizes. Present semiconductor technology now permits single-chip microprocessors with many millions of transistors, operating at speeds of tens (or even hundreds) of MIPS (millions of instructions per second), to be packaged in relatively small, air-cooled semiconductor device packages. As integrated circuit devices, microprocessors and other related components are designed with increased capabilities and increased speed, additional heat is generated from these components. As packaged units and integrated circuit die sizes shrink, the amount of heat energy given off by a component for a given unit of surface area is also on the rise. The majority of the heat generated by a component, such as a microprocessor, must be removed from the component to keep the component at an operating temperature. If the heat generated is not removed from the component, the heat produced can drive the temperature of the component to levels that result in failure of the component. In some instances, the full capability of certain components can not be realized since the heat the component generates at the full capability would result in failure of the component.
A seemingly constant industry trend for all electronic devices, and especially for personal computing, is to constantly improve products by adding increased capabilities and additional features. For example, the electronics industry has seen almost a 50 fold increase in processing speed over the last decade. Increasing the speed of a microprocessor increases the amount of heat output from the microprocessor. Furthermore, as computer related equipment becomes smaller and more powerful, more components are being used as part of one piece of equipment. As a result, the amount of heat generated on a per unit volume basis is also on the increase. A portion of an amount of heat produced by semiconductors and integrated circuits within a device must be dissipated to prevent operating temperatures that can potentially damage the components of the equipment, or reduce the lifetime of the individual components and the equipment.
An integrated circuit has a front side and a back side. The front side of the integrated circuit includes leads for inputs, outputs and power to the integrated circuit. Leads include many forms, including pins and balls in a ball grid array. The leads of an integrated circuit are attached to pads on another device such as a printed circuit board. For example, an integrated circuit that includes a die having a microprocessor therein has a front side that is attached to the pads on a motherboard. A heat sink is attached to the back side of the integrated circuit. In other words, the heat sink is attached to the back side major surface and extends away from a printed circuit board to which the integrated circuit is mounted. Therefore, generally a major portion of the heat generated is extracted from the back side of the integrated circuit with the die therein.
There is generally a limitation on the amount of heat that can be extracted from the back side of the integrated circuit die, because of the thermal resistance induced by the thermal interface materials (such as a silicon die, any thermal grease, adhesives or solders) used between the back side of the integrated circuit die and the heat sink. Most heat sinks are formed from copper or aluminum. The materials used currently as heat sinks have a limited ability to conduct heat. Relatively large fin structures are also provided to increase the amount of heat removed via conduction. Fans are also provided to move air over the fin structures to aid in the conduction of heat. Increasing the size of the fin structure increases the volume of the heat sink, and generally also increases the stack height of the heat sink. In many electronic devices, the overall size of the heat sink is generally limited by volume constraints of the housing. For example, in some mobile products such as laptop computers and ultra-mobile computers, small stack heights are required.
The use of aluminum and copper heat sinks with fin structures are now approaching their practical limits for removal of heat from a high performance integrated circuit, such as the integrated circuits that include dies for microprocessors. When heat is not effectively dissipated, the dies develop “hot spots” or areas of localized overheating. Ultimately, the circuitry within the die fails. When the die fails, the electrical component also fails.
In some instances, aluminum and copper heat sinks are replaced with a diamond heat sink. Diamond heat sinks are difficult to manufacture. One aspect of a diamond heat sink is that one major surface of the heat sink must be ground smooth to provide a good thermal connection at a thermal interface. Grinding or smoothing diamond is time consuming. Diamond heat sinks are also expensive.
The description set out herein illustrates the various embodiments of the invention, and such description is not intended to be construed as limiting in any manner.